Zoom lens and imaging apparatus

Abstract

A zoom lens comprises, in order from the object side: a first lens group that has a positive refractive power; a second lens group that has a negative refractive power; and a third lens group that has a positive refractive power. Zooming is performed by changing spaces between the first to third lens groups during zooming from a wide-angle end to a telephoto end. The third lens group includes, in order from the object side, a positive lens group, having a positive refractive power, and a negative lens group, disposed to be close to the image side thereof and having a negative refractive power, with an air gap, which is widest in the third lens group, interposed therebetween. The third lens group satisfies the condition −0.45<fGF/fGR<−0.10, where fGF is a focal length of the positive lens group, and fGR is a focal length of the negative lens group.

What is claimed is: 
     
       1. A zoom lens comprising, in order from the object side:
 a first lens group that has a positive refractive power; 
 a second lens group that has a negative refractive power; and 
 a third lens group that has a positive refractive power, 
 wherein zooming is performed by changing spaces between the first to third lens groups during zooming from a wide-angle end to a telephoto end, 
 wherein the third lens group includes, in order from the object side, a positive lens group, which has a positive refractive power, and a negative lens group, which is disposed to be close to the image side thereof and has a negative refractive power, with an air gap, which is widest in the third lens group, interposed therebetween, 
 wherein the negative lens group includes a cemented lens which has a negative refractive power and which is formed of, in order from the object side, a positive lens and a negative lens, and a second positive lens, and 
 wherein the following Conditional Expression (1) is satisfied
   −0.45< fGF/fGR<− 0.10,  (1)
 
 
 where
 fGF is a focal length of the positive lens group, and 
 fGR is a focal length of the negative lens group. 
 
 
     
     
       2. The zoom lens according to  claim 1 , wherein the following Conditional Expression (2) is further satisfied
   0.1< L 3/ ft< 0.2,  (2)
 
 where
 L 3  is a length of the third lens group on an optical axis, and 
 ft is a focal length of the whole system at the telephoto end of the zoom lens. 
 
 
     
     
       3. The zoom lens according to  claim 2 ,
 wherein the negative lens group includes the cemented lens which is disposed to be closest to the object side, and is formed of the positive lens which is convex toward the object side and the negative lens which is concave toward the image side, and 
 wherein the following conditional expressions (3) and (4) are satisfied
   0.2<( RLR 1− RLR 2)/( RLR 1+ RLR 2)<0.8,  (3)
 
   and 
     ndLR 2>1.72,  (4)
 
 
 where
 RLR 1  is a radius of curvature of a surface of the cemented lens closest to the object side, 
 RLR 2  is a radius of curvature of a surface of the cemented lens closest to the image side, and 
 ndLR 2  is a refractive index of the negative lens at the d-line. 
 
 
     
     
       4. The zoom lens according to  claim 3 , wherein the following Conditional Expression (5) is further satisfied
     νdp/νdn> 1.18,  (5)
 
 where
 νdp is an Abbe number of the positive lens constituting the cemented lens at the d-line, and 
 νdn is an Abbe number of the negative lens constituting the cemented lens at the d-line. 
 
 
     
     
       5. The zoom lens according to  claim 2 , wherein the negative lens group includes, in order from the object side, the cemented lens which has a negative refractive power and is formed of the positive lens which is convex toward the object side and the negative lens which is concave toward the image side, and a second positive lens. 
     
     
       6. The zoom lens according to  claim 1 , wherein the positive lens group comprises a plurality of lenses. 
     
     
       7. The zoom lens according to  claim 1 , wherein an aperture stop is located within the positive lens group. 
     
     
       8. The zoom lens according to  claim 1 , wherein the following Conditional Expression (1′) is satisfied
   −0.35< fGF/fGR<− 0.20.  (1′)
 
 
     
     
       9. The zoom lens according to  claim 1 , wherein at least a part of one lens group among the first, second, and third lens groups is configured to be shifted in a direction which is substantially perpendicular to an optical axis. 
     
     
       10. An imaging apparatus comprising:
 a zoom lens that includes, in order from the object side, a first lens group which has a positive refractive power, a second lens group which has a negative refractive power, and a third lens group which has a positive refractive power; and 
 an imaging device that converts an optical image, which is formed by the zoom lens, into an electrical signal, 
 wherein the zoom lens performs zooming by changing spaces between the first to third lens groups during zooming from a wide-angle end to a telephoto end, 
 wherein the third lens group includes, in order from the object side, a positive lens group, which has a positive refractive power, and a negative lens group, which is disposed to be close to the image side thereof and has a negative refractive power, with an air gap, which is widest in the third lens group, interposed therebetween, 
 wherein the negative lens group includes a cemented lens which has a negative refractive power and which is formed of, in order from the object side, a positive lens and a negative lens, and a second positive lens, and 
 wherein the following Conditional Expression (1) is satisfied
   −0.45< fGF/fGR<− 0.10,  (1)
 
 
 where
 fGF is a focal length of the positive lens group, and 
 fGR is a focal length of the negative lens group. 
 
 
     
     
       11. The imaging apparatus according to  claim 10 , wherein the following Conditional Expression (2) is further satisfied
   0.1< L 3/ ft< 0.2,  (2)
 
 where
 L 3  is a length of the third lens group on an optical axis, and 
 ft is a focal length of the whole system at the telephoto end of the zoom lens. 
 
 
     
     
       12. The imaging apparatus according to  claim 11 ,
 wherein the negative lens group includes the cemented lens which is disposed to be closest to the object side, and is formed of the positive lens which is convex toward the object side and the negative lens which is concave toward the image side, and 
 wherein the following conditional expressions (3) and (4) are satisfied
   0.2<( RLR 1− RLR 2)/( RLR 1+ RLR 2)<0.8,  (3)
 
   and 
     ndLR 2>1.72,  (4)
 
 
 where
 RLR 1  is a radius of curvature of a surface of the cemented lens closest to the object side, 
 RLR 2  is a radius of curvature of a surface of the cemented lens closest to the image side, and 
 ndLR 2  is a refractive index of the negative lens at the d-line. 
 
 
     
     
       13. The imaging apparatus according to  claim 12 , wherein the following Conditional Expression (5) is further satisfied
   ν dp/νdn> 1.18,  (5)
 
 where
 νdp is an Abbe number of the positive lens constituting the cemented lens at the d-line, and 
 νdn is an Abbe number of the negative lens constituting the cemented lens at the d-line. 
 
 
     
     
       14. The imaging apparatus according to  claim 11 , wherein the negative lens group includes, in order from the object side, the cemented lens which has a negative refractive power and is formed of the positive lens which is convex toward the object side and the negative lens which is concave toward the image side, and a second positive lens. 
     
     
       15. The imaging apparatus according to  claim 10 , wherein the positive lens group comprises a plurality of lenses. 
     
     
       16. The imaging apparatus according to  claim 10 , wherein an aperture stop is located within the positive lens group. 
     
     
       17. The imaging apparatus according to  claim 10 , wherein the following Conditional Expression (1′) is satisfied
   −0.35< fGF/fGR<− 0.20.  (1′)
 
 
     
     
       18. The imaging apparatus according to  claim 10 , wherein at least a part of one lens group among the first, second, and third lens groups is configured to be shifted in a direction which is substantially perpendicular to an optical axis. 
     
     
       19. The imaging apparatus according to  claim 10 , wherein the imaging device includes a photoelectric conversion device. 
     
     
       20. The imaging apparatus according to  claim 19 , wherein the photoelectric conversion device is selected from the group including a CCD and a CMOS.